1. Field
This invention relates generally to pressurized water nuclear reactors and, more particularly, to steam generators for pressurized water reactors.
2. Description of Related Art
In a nuclear reactor for power generation, such as a pressurized water reactor, heat is generated by fission of a nuclear fuel such as enriched uranium, and transferred into a coolant flowing through a reactor core. The core contains elongated nuclear fuel rods mounted in proximity with one another in a fuel assembly structure, through and over which the coolant flows. The fuel rods are spaced from one another in co-extensive parallel arrays. Some of the neutrons and other atomic particles released during nuclear decay of the fuel atoms in a given fuel rod pass through the spaces between fuel rods and impinge on fissile material in adjacent fuel rods, contributing to the nuclear reaction and to the heat generated by the core.
Moveable control rods are dispersed throughout the nuclear core to enable control of the overall rate of the fission reaction, by absorbing a portion of the neutrons passing between fuel rods, which otherwise would contribute to the fission reaction. The control rods generally comprise elongated rods of neutron absorbing material and fit into longitudinal openings or guide thimbles in the fuel assemblies running parallel to and between the fuel rods. Inserting a control rod further into the core causes more neutrons to be absorbed without contributing to fission in an adjacent fuel rod; and retracting the control rods reduces the extent of neutron absorption and increases the rate of the nuclear reaction and the power output of the core.
FIG. 1 shows a simplified conventional nuclear reactor primary system, including a generally cylindrical pressure vessel 10 having a closure head 12 enclosing a nuclear core 14 that supports the fuel rods containing the fissile material. A liquid coolant, such as water, is pumped into the vessel 10 by pump 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18 typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown) such as a steam driven turbine generator or industrial process steam application. A pressurizer 22 is included to maintain the pressure of the system to ensure the coolant does not bulk boil. The reactor coolant is then returned to the pump 16 completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20.
Commercial power plants employing this design are typically on the order of 1,100 megawatts electrical output or more. More recently, Westinghouse Electric Company LLC has proposed a small modular reactor in the 200-300 megawatt class electrical output. The small modular reactor is an integral pressurized water reactor with all primary components located inside the reactor vessel. Required component size and fabrication methods typically make the steam generator one of the larger primary system components; therefore, incorporating the steam generator within the reactor vessel would make the vessel unwieldy, both from a manufacturing standpoint as well as from a service perspective. Thus, there is a need for a new steam generator design that will reduce the size of the steam generator components that would benefit from being housed within the reactor vessel.
Accordingly, a new compact steam generator design is desired that will maintain the efficiencies of traditional pressurized water reactor steam generators with no sacrifice in safety.
Furthermore, a new compact steam generator design is desired that will reduce the overall size of the components that need to be stored within the reactor containment.